The movements at the shoulder are complex. Here we look at the bones, joints and muscles that make up the shoulder and support it.
Three bones come together to form the shoulder girdle:
Humerus (Upper arm bone)
Scapula (Shoulder blade)
The scapula and clavicle are not attached to the stable structure of the spine.
One end of the clavicle attaches to the sternum (there is a cartilage disc between).
The other end of the clavicle attaches to the scapula (bound by ligaments) at the acromion process (This is the acromioclavicular (AC) joint, the bump at the top of the shoulder).
The humerus is attached to the scapula and triggers movement of the scapula when it reaches the end of its range of motion (usually after around 90 degrees of lift).
Elevation – up
Depression – down
Protraction – slide to the front towards the rib cage
Retraction – slide back so that the two scapulae move closer to each other on your back
Tilt sideways – we see this movement in high plank or chaturanga
Follows the scapula in most of its movements:
Rotation (unlike the scapula) – not particularly large (but allows the reversed prayer yoga position).
Muscles impacting the Humerus
There is a lot of flexibility at the shoulder joint (e.g. compared to the hip joint). There therefore needs to be stability provided from the muscles:
Pectoralis Major – large mover of the humerus (flexor, extender and internal rotator), close to the surface. Attach from the clavicle to the sternum and then down to some of the lower ribs.
Latissimus Dorsi – large mover of the humerus (internal rotator, extender, adductor), close to the surface at the back of the body and attaches to the sacrum, lower ribs and up the humerus, draping over the scapula.
Teres Major – Assist the latissimus dorsi in adduction and internal rotation.
Deltoids – Attached around the clavicle, acromion and scapula. Assists in flexion, internal rotation, extension, external rotation, and adduction.
Rotator Cuff – deeper muscles that stabilize the joint but still allows flexibility. Tears of these muscles are common. This group consists of 4 muscles:
Muscles impacting the Scapula
Trapezius muscle – covers a large portion of the upper back and contributes to upward rotation of the scapula.
Rhomboids – Sit between the shoulder blades. Assists in downward rotation and retraction of the scapula.
Levator scapulae – Downward rotator of the scapula.
Pectoralis minor – located at the front of the rib cage and attaches to the coracoid process. It is a downward rotator and depressor of the scapula.
Serratus anterior – The muscle heads back between the scapula and the rib cage to attach onto the inner border of the scapula. The muscle protracts and upwardly rotates the scapula.
Shoulder bone shape
There are variations on bone shape from person to person.
Three types of scapula which are described by how the acromion process sits. This then results in a different amount of space for the humerus to move.
Yoga Implications (Chaturanga)
If the shoulders are brought lower than the elbows in this position then the scapula is out of place causing strain on the shoulder muscles (including rotator cuffs and biceps).
The further forward the shoulders are from the hands, he more strain on the shoulders because the bulk of the body is too far forward to be supported by the hands.
Be careful in the transition to downward dog:
Practicing too much, too soon (e.g. skip some of the vinyasa sections if you are new to the practice).
Options for beginners:
The rotator cuff muscles work hard in Chaturanga, Up Dog and Down Dog. They work even harder through the jump forward, back or through. Take care with these positions and be mindful of the shoulders.